The applicant of the present application claims priority date of related Taiwan application No. 090111861 filed at May 17, 2001, and entitled xe2x80x9cDual Band Slot Antenna.xe2x80x9d
1. Field of the Invention
The present invention relates to a dual band antenna, and more particularly, to a dual band slot antenna containing two slots for creating resonance within distinct frequency bands.
2. Description of the Prior Art
Wireless transmission has become a required function for today""s mobile devices, such as laptop computers and handhelds. FIG. 1 illustrates a typical planar slot antenna for use in a mobile device for transmitting and receiving wireless signals. Slot antenna 1 includes a conducting plate 10 in which an elongate opening or slot 11 is formed. A coaxial cable 14 is connected to the conducting plate 10 by connecting the inner conductor to feed point 12 and connecting the outer conductor to ground 13. When situated in electromagnetic fields, electric currents will be induced on the conducting plate 10 and resonance is created along the slot 11. The induced currents carry encoded signals according to the protocol utilized for wireless transmission and are collected and received at feed point 12 by the coaxial cable 14 for further decoding.
Similarly, when the coaxial cable 14 feed encoded signals to the conducting plate 10 through feed point 12, electric currents are generated on the conducting plate 10 and resonance is created along the slot 11 so that electromagnetic waves carrying the encoded signals can be radiated away. As a general rule, the longer is the slot 11, the lower is the resonance frequency, and vice versa. By adjusting the shape and dimension of the slot 11, one is able to have the slot antenna 1 function within a desired frequency range according to protocol specification.
Currently there are several protocols available for establishing wireless transmission, each utilizing a particular frequency band. For example, Bluetooth and IEEE 802.11b both operate at 2.4 GHz, while GPRS operates at 900 MHz and 1800 MHz, and IEEE 802.11a at 5.5 GHz. Although the prior art slot antenna 1 illustrated in FIG. 1 can be made to operate at a wide variety of frequency ranges, it can only function for one particular frequency range at one time. That is, the slot antenna 1 is a monoband antenna and is therefore limited in its application. It is needed in this regard to have a dual band slot antenna that can transmit and receive signals of two frequency bands.
It is therefore a primary objective of the claimed invention to provide a dual band planar slot antenna to overcome the above-mentioned shortcoming of the prior art.
According to one embodiment of the claimed invention, the antenna comprises a metallic plate having two elongate slots. The first slot and the second slot are longitudinally parallel and close to each other. A coaxial cable feeds signals across the first slot. A securing structure securely and precisely fixes the coaxial cable onto the metallic plate at a desired position. The first slot and the second slot are electrically connected to the coaxial cable so that, by sharing the same feed, the first slot is used to transmit and receive radio signals of a first frequency band and the second slot is used to transmit and receive radio signals of a second frequency band.
According to another embodiment of the claimed invention, the antenna comprises a metallic plate having two elongate slots formed in oblique surfaces respectively.
These and other objectives of the claimed invention will no doubt become obvious to any skilled artist in this field after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.